In most current color picture tube types, a peripheral frame supporting a shadow mask is suspended in a faceplate panel by means of springs that are welded either directly to the frame or to plates which in turn are welded to the frame. In the directly welded version, the springs are usually made of bimetallic materials; and in the plate version, the plates are bimetallic. As the springs or plates become heated by transfer of heat from the mask through the frame, the bimetallic materials expand differently, thereby bending the springs or plates to cause movement of the mask-frame assembly toward a screen disposed on the panel. It is also known to use the geometric structure of the springs to cause this same motion towards the screen by action of the force of the expanding mask-frame assembly against the springs.
It is common to use either three of four springs to support a mask-frame assembly within a rectangular faceplate panel of a tube. In a three-spring support system, one spring is usually located at the upper center of the mask, and the other two springs are located along the sides of the tube between the centers of the sides of the mask and the lower two corners of the mask. In a four-spring support system, springs are usually located at the top and bottom centers of the mask and at the left and right centers of the mask. In both the three- and four-spring support systems, as described above, it is possible for the mask-frame assembly to twist slightly and shift relative to the faceplate, during tube manufacture and/or operation.
A known means for minimizing twisting and shifting of a mask-frame assembly uses spring supports at the four corners of the frame. Embodiments for achieving such corner support are shown in U.S. Pat. No. 4,723,088, issued to Sone et al. on Feb. 2, 1988, in U.S. Pat. No. 4,728,853, issued to Sone et al. on Mar. 1, 1988, and in U.S. Pat. No. 4,884,005, issued to Kornaker et al. on Nov. 28, 1989. Use of a four-spring corner support system has another advantage. With a corner support system, a lighter frame can be used. This results not only in a cost reduction, but also yields better performance for mask-doming and long-term temperature compensation in a completed tube.
U.S. Pat. No. 4,723,088 shows a mask frame having truncated corners with supports at each corner. The supports are bent plates including three sections. A first section is welded to the frame. A second section extends at an angle from the first section toward a skirt of a faceplate panel. A third section extends from the second section and includes an aperture that engages a metal stud embedded in the panel sidewall.
U.S. Pat. NO. 4,728,853 discloses a mask-frame assembly support which includes two members welded together. One member, having a flat plate shape, is welded to a mask frame. The second member includes three sections. A first section is welded to the first member. A second section angles from the first section, and an apertured third section engages a support stud in the panel sidewall.
U.S. Pat. No. 4,884,005 shows a mask without a frame. Auxiliary brackets are used to reinforce the corners of the mask and, at each corner, a spring is attached to a bimetal element which, in turn, is attached to a bracket some distance from the corner of the tube. The free ends of the springs extend into the corners where they rest on spherical ends of studs. The ends of the retaining springs are bent so as to be perpendicular to the longitudinal axis of the studs.
A problem encountered with many prior art support systems is that they may shift when subjected to shock and vibration. Therefore, there is a need for improvements in mask support systems that will reduce their susceptibility to such shifts. The present invention provides an improvement in tubes, making them less affected by shock and vibration than are encountered in tubes with the prior art support systems.